Spider's Personalities Determine Their Job Performance

Aggressive spiders defend, hunt, and build, while docile ones take care of young.

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Anelosimus studiosus spiders, like this one, all look the same, but each has one of two distinct personality types: aggressive or docile.

PHOTOGRAPH BY JUDY GHALLAGHER

To close that business deal, you have to be aggressive. To be a good doctor or teacher, you need to be calm and nurturing. While personality almost always plays a big role in what jobs people choose and excel at, a new study says personality is also important for spiders—and maybe other social critters, such as ants or bees, too.

A small number of species of spiders are social, working and living together in a colony just like ants and bees. Some of those spiders have personalities too, and it not only determines which job an individual does for its colony, but also how good it is at that job.

Researchers found that aggressive spiders took on the tasks of killing prey, building webs, and defending the colony, while docile spiders tended to care for the baby spiders. The spiders whose personalities were compatible with their job duties were also better at their respective jobs.

"We can see very strongly that personality matters," says Colin Wright of the University of Pittsburgh, who led the study. "It's probably the best example of how personality can shape or organize labor within a colony."

It's All About Personality

For social creatures such as ants or bees, jobs are divided based on physical characteristics. For example, the bigger ants are the ones who carry food and defend the colony.

But there hasn't been much evidence that shows how personality affects labor in a colony, Wright says. In fact, only in the past couple of decades have scientists begun to unravel the psyches of insects and spiders. Bees and wasps, for instance, have varying levels of aggressiveness, boldness, and the urge to explore.

In the new study, which the team reports in this week's journal Proceedings of the National Academy of Sciences, Wright and his colleagues studied female Anelosimus studiosus, a type of tangle web spider found in North and South America. Although the spiders all look the same, each has one of two distinct personality types: aggressive or docile.

To identify personality type, the researchers placed two spiders in the middle of a box. If, after an entire day, the two spiders moved close together, they were deemed docile and cooperative. But if they went to opposite corners, then at least one of them must be aggressive, since an aggressive spider would need personal space. Each of those spiders were then paired with a known docile spider to determine if they were indeed aggressive.

The researchers then kept tabs on which job each personality type took. The aggressive spiders spent most of their time defending the colony, building webs, and capturing prey. Meanwhile, the majority of docile spiders spent most of their time looking after the brood.

The researchers also found that personality aligned with job performance. The aggressive ones were better at fending off an intruder, repairing a broken web, and capturing a cricket for food. But they were bad at taking care of their young, resulting in lower survival rates. They also inadvertently killed the offspring much more often than docile spiders did.

Your Friendly Neighborhood Spider-Parent

"One of the more surprising things was to know [what] good parents the docile individuals were," Wright says.

Previous research showed that colonies were more successful when they were composed of a mix of aggressive and docile spiders, but it wasn't clear what role the docile spiders played, he says. "For a long time we weren't quite sure what the purpose of the docile spider was." Some scientists thought they were lazy freeloaders.

Personality may play just as big a role in how tasks are distributed for other social insects, he says. The variety and complexity of labor division that aligns with physical differences may also exist with personality differences.

The study "does a nice job of linking the idea that variation in individual personality contributes to which task individuals gravitate to and excel in," says Jennifer Fewell of Arizona State University. "Division of labor is often assumed to be a feature only of highly evolved societies, such as the ants and honeybees—and humans. However, it is a fundamental organizing principle across social species." This study emphasizes that divvying up work is really a general feature of animal societies.

While these spiders don't directly reveal anything about human behavior, you can't help but draw a connection, Wright says. "The more animals you study, the more you realize you're an animal yourself."